Mapping 2D Sliding Mechanisms of Bilayer and Bulk Ni-doped MoS₂ from First Principles

The van der Waals forces between layers of 2D materials allow for easy sliding, which is used in solid lubrication and also relevant to sliding ferroelectricity, strain engineering, stacking of 2D materials, and nanomechanical devices. Motivated by our previous study [arXiv:2209.15629] in 1D, we explore the 2D sliding potential energy surface (PES) landscape of Ni-doped MoS₂ which is found to have favorable properties for space lubrication. We use previously identified stable and metastable doped structures: Mo/S substitutions and octahedral/tetrahedral intercalations. We determine favored sliding pathways in different directions from the PES and nudged elastic band calculations. The PES have extrema generally related to high-symmetry stackings, but the octahedral intercalated structure also has deep minima away from symmetric points where the structure changes significantly. We analyze the sliding PES in terms of bonding changes, symmetry breaking, relation between bilayer and bulk interactions, and the effects of load. We also compare our results to the registry index model, as generalized to the case of doped materials. These findings augment our understanding of sliding in doped 2D materials and how it could be tuned.